The present invention generally relates to printer apparatus and methods and more particularly relates to a printer apparatus adapted to reduce cross-talk between ink channels therein, and method thereof.
An ink jet printer produces images on a receiver medium by ejecting ink droplets onto the receiver medium in an image-wise fashion. The advantages of non-impact, low-noise, low energy use, and low cost operation in addition to the capability of the printer to print on plain paper are largely responsible for the wide acceptance of ink jet printers in the marketplace.
However, one problem associated with piezoelectric ink jet printers is placement errors of the ink droplets on the receiver medium. Such errors are due, for example, to mechanical and/or hydraulic coupling (i.e., "cross-talk") between side-by-side ink channels comprising the ink jet printer's printhead. That is, each ink channel, which is defined by a pair of parallel side walls made of the piezoelectric material, may share a common side wall with an adjoining channel. When an ink channel is selected for ink ejection therefrom, an electrical pulse is supplied to the side walls defining the ink channel in order to cause movement of the side walls. A pressure surge occurs in the ink channel as the side walls move, which pressure surge causes an ink droplet to eject from the ink channel. However, movement of the side walls associated with the selected ink channel in order to cause a pressure surge therein may inadvertently cause a pressure surge in an adjoining non-selected ink channel. Therefore, the pressure surge produced in the adjoining non-selected channel may inadvertently eject an ink droplet from the non-selected channel. This is so because each channel shares a common side wall with an adjoining channel. Moreover, pressure change in a channel selected for actuation may affect pressure in a remote non-adjoining channel due to a so-called "domino effect". That is, if a first channel is selected for actuation, a second channel adjoining the first channel but not selected for actuation will see change in pressure because the first and second channels share common side walls. Accordingly, a third channel not selected for actuation but adjoining the second channel will see some change in pressure because the second and third channels share common side walls. This phenomenon, referred to herein as the "domino effect" occurs for the fourth channel, the fifth channel, and so on. Eventually, this propagating pressure surge, although diminishing in intensity, may reach another actuated channel which is being intentionally actuated simultaneously with the first channel to achieve the desired droplet image pattern. However, this second actuated channel will not only experience the expected pressure surge caused by its actuation, but may also experience an additional unexpected pressure surge component caused by the "domino effect", which is undesirable. Such mechanical coupling (i.e., cross-talk) between the channels interferes with precise ejection of ink droplets, which in turn reduces accuracy of ink droplet placement on the receiver medium.
In addition, when ink in a selected ink channel is pressurized, the pressure surge therein may be hydraulically communicated to ink in another channel because each ink channel is in fluid communication with a common manifold holding a supply of the ink. This latter phenomenon results in hydraulic cross-talk, which in turn may lead to inadvertent ejection of an ink droplet. In other words, hydraulic cross-talk causing inadvertent ejection of an ink droplet from the non-selected channel will also produce ink droplet placement errors on the receiver medium. These ink droplet placement errors in turn produce image artifacts such as banding, reduced sharpness, extraneous ink spots, ink coalescence and color bleeding.
Techniques to reduce cross-talk are known. An ink jet printhead having low mechanical over-coupling from one channel to another is disclosed in U.S. Pat. No. 4,842,493 titled "Piezoelectric Pump" issued Jun. 27, 1989 in the name of Kenth Nilsson. This patent discloses a piezoceramic wafer into which grooves have been sawed from the upperside and underside of the wafer. The grooves on the upperside and underside of the wafer lay offset relative to one another and partially overlap. The grooves on the upperside of the wafer eject ink droplets while the grooves on the underside of the wafer contain only air. In this manner, deformation of the walls of one ink groove is hardly at all transmitted to another ink groove because adjacent ink grooves are separated by an intervening air-filled groove.
Although the Nilsson device provides for low "cross-talk", the Nilsson device does not appear to provide means for reducing hydraulic cross-talk and also does not appear to provide means to further reduce mechanical cross-talk to a level less than that achieved only with the intervening air-filled grooves.
Therefore, there has been a long-felt need to provide a printer apparatus suitably adapted to reduce cross-talk between ink channels therein, and method thereof.